The recommended dose of prazosin is 0.5mg/kg (1mg/lb) twice daily. However, it is not known whether or not higher doses are safe. Doses up to 2mg/kg (4mg/lb) have been used successfully in some cases; however, there may be adverse effects such as seizures at these high dosages.
There are no long term studies on the safety of prazosin dosages greater than 4mg/kg (8mg/lb). There are reports of death occurring with doses over 10mg/kg (20mg/lb), but these were all in patients with severe liver disease. Other side effects include nausea, vomiting, diarrhea, constipation, headache and dizziness. These symptoms usually subside within 24 hours after discontinuation of treatment.
Nausea, vomiting, diarrhea, constipation, headache and dizziness are common side effects of prazosin. They generally subside within 24 hours after discontinuation of treatment. If you experience any of these symptoms while taking prazosin please contact your doctor immediately. For most people they will go away without medical attention.
Side effects such as nausea and vomiting are very rare when taken in appropriate amounts and with the proper frequency.
Severe side effects are more common at higher dosages. These include slowed breathing, fainting, excessively slow heart rate (bradycardia), low blood pressure and death. Death is very unlikely unless you’ve taken around 20mg/kg (40mg/lb) or higher. If you experience any of these severe side effects stop taking prazosin immediately and seek immediate medical attention.
If you experience any other side effects, contact your doctor as soon as possible.
Prazosin may increase your risk of having a stroke or heart attack by affecting the electrical activity in your heart. Your heart may beat too fast, irregularly or not at all due to prazosin. If you have heart or blood vessel problems it is recommended that you stop taking prazosin. If you experience chest pain, shortness of breath, fainting or dizziness while taking prazosin, seek medical attention immediately.
Prazosin may make your body more sensitive to temperature extremes and the sun. Avoid staying in high temperature areas for extended periods of time while taking this medication. Avoid prolonged sun exposure as it may cause an increase in your blood pressure and cause heat stroke. If you notice a severe increase in your body temperature, seek medical attention immediately.
Prazosin may cause an allergic reaction in some people. Stop taking the medication and seek immediate medical attention if you notice hives, swelling of the face or throat, trouble breathing or swallowing, or irregular heartbeat.
If you have seizures, any intentional or accidental overdose of prazosin may cause your seizures to become worse.
The elderly are more susceptible to side effects such as drowsiness and slow heart rate. They are also more susceptible to experiencing decreased blood pressure. Due to changes in metabolism, the elderly may experience a higher risk of side effects when taking prazosin. Follow your doctor’s instructions carefully and contact them if you have any concerns.
Prazosin should not be taken by women who are pregnant or breastfeeding and individuals who are under 18 years of age.
Prazosin may cause drowsiness, dizziness or lightheadedness. Do not drive or operate heavy machinery until you know how prazosin affects you.
Avoid drinking alcohol while taking prazosin. Alcohol may increase some of the side effects of the medication.
Last Updated: 8/4/2018
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